When threatened with fact-checking, politicans really will lie less often.

Imagine you’re a state legislator. Over the course of a couple of months you get three letters that say things like this:

We are writing to let you know about an important research project. As you may know, the national fact-checking organization PolitiFact has created an affiliate in [legislator’s state]. Our research project examines how elected officials in your state are responding to the presence of this fact-checking organization during this campaign season. PolitiFact examines statements made by politicians and then rates their accuracy and truthfulness on a scale that ranges from “true” to “pants on fire”…In particular, we are writing to notify you that we are studying how elected officials react to the presence of a PolitiFact affiliate in their state.

What would you do?

According to the researchers who sent these letters to a random subset of state legislators in nine different states, you will make fewer inaccurate claims. Those researchers are Dartmouth’s Brendan Nyhan and the University of Exeter’s Jason Reifler. They conducted the first real-world experiment of whether the potential for fact-checking can actually make politicians more honest. In their new paper, they write:

Our results indicate that legislators who were sent our treatment letters were substantially less likely to receive negative PolitiFact rating or to have their accuracy questioned publicly.

To be sure, relatively few legislators received a negative rating overall. Nevertheless, legislators who got these letters were significantly less likely to say things that Politifact ended up questioning. And the real effects may be larger, since Nyhan and Reifler do not know for sure which legislators read the letters. But since legislators were randomly assigned to get letters, they can have confidence that it was the letters that mattered. Even the possibility of being fact-checked made a difference.